Railroad Roundhouse, Atlanta, Georgia, 1864 Link to picture of the area after the war: . OVERSIZE IMAGE
That's a good question, Al. I wondered the same thing, but couldn't find a picture of the entrance. It must have been around the back side. Here's a shot from a different angle, with more tracks.
Yes. I wonder how they powered the turntable, or whatever you call it, in 1864. Horses? Steam? I can't find a picture.